In a voice network, each subscriber group has a common ring bus and a test bus. Moreover, each subscriber in the subscriber group has an independent subscriber line interface circuit (SLIC).
On an analog subscriber board, the basic functions of talking and ringing must be provided for each subscriber in a group. In addition, the different functions of testing and monitoring should be provided selectively for subscriber according to the requirements of different voice networks.
In order to perform these functions, three relays are provided for each subscriber on an analog subscriber board of the prior art, which are connected to the ring bus, the test bus, the subscriber line interface circuit and the subscriber line respectively, as shown in FIG. 1.
FIG. 1 is a schematic diagram showing the connection of relays on an analog subscriber board of the prior art, wherein only three relays K1, K2, K3 relevant directly to controlling and realizing the various functions of a voice network, as well as ring bus 2, test bus 3, subscriber line interface circuit (SLIC) 1 and subscriber line 4 are shown, while other parts being not in the drawing. In this drawing, subscriber line interface circuit (SLIC) 1 is connected to movable contact point K11 of relay K1, ring bus 2 is connected to another movable contact point K12 of relay K1, test bus 3 is connected to static contact point K33 of relay K3, subscriber line 4 is connected to movable contact point K21 of relay K2 and movable contact point K32 of relay K3 simultaneously. Static contact point 13 of relay K1 is connected to static contact point K23 of relay K2, another movable contact point K22 of relay K2 is connected to another movable contact point K31 of relay K3.
In FIG. 1, for simplification, ring bus 2, test bus 3, subscriber line interface circuit 1 and subscriber line 4 are all indicated by single-lines. In an actual voice network all lines are constituted of double-lines. Especially, subscriber line interface circuit 1 and subscriber line 4 should be constituted of the pair of TIP/RING double-line. Correspondingly, the contact points of various relays should be twice as many as shown in FIG. 1.
In FIG. 1, for simplification, only one subscriber is shown in the connection schematic diagram. In an actual application, subscriber line interface circuit 1 and subscriber line 4 are for each subscriber solely, but ring bus 2 and test bus 3 are common to all subscribers in a group. A plurality of analog voice functions can be provided by providing three relays K1, K2, K3 for each subscriber respectively.
When subscriber line 4 of a subscriber is connected to subscriber line interface circuit 1 of the subscriber, the analog subscriber board realizes the talking/idle function of the subscriber; when subscriber line 4 is connected to ring bus 2, the analog subscriber board realizes the ringing function of the subscriber; when subscriber line 4 is connected to test bus 3 and subscriber line interface circuit 1 of the subscriber simultaneously, the analog subscriber board realizes the talking monitoring function for the subscriber; when subscriber line 4 is connected to ring bus 2 and test bus 3 simultaneously, the analog subscriber board realizes the ringing monitoring function for the subscriber; when test bus 3 is connected to subscriber line interface circuit 1 of a subscriber, the analog subscriber board realizes the function for testing the subscriber line interface circuit of the subscriber; when test bus 3 is connected to ring bus 2, the analog subscriber board realizes the ring testing function; when test bus 3 is connected to subscriber line 4 of a subscriber, the analog subscriber board realizes the function for testing the subscriber line of the subscriber.
Table 1 shows the realization of the various functions of the analog subscriber board in FIG. 1. Various functions can be realized by controlling the states of three relays K1, K2, K3 (that is, the movable contact point is turned on) respectively.
TABLE 1Realization of Various Functions of Analog Subscriber Board in FIG.1State of K1State of K2State of K3FunctionK11K21K31talking/idleK12K21K31ringingK11K21K32monitoring talkingK12K21K32monitoring ringingK11K22K31testing subscriberline interface circuitK12K22K31testing ring—K22K32testing subscriber line
More specifically, when relay K2 is controlled to turn on movable contact point K21 connected to subscriber line 4, the analog subscriber board realizes the basic functions (talking/idle or ringing) or the monitoring functions (talking monitoring or ringing monitoring), wherein when relay K3 turns on movable contact point K31 connected to relay K2, the analog subscriber board realizes correspondingly the talking/idle function or ringing function respectively according to that relay K1 turns on movable contact point K11 connected to subscriber line interface circuit 1 or turns on movable contact point K12 connected to ring bus 2; when relay K3 turns on movable contact point K32 connected to subscriber line 4, the analog subscriber board realizes correspondingly the talking monitoring function or ringing monitoring function respectively according to that relay K1 turns on movable contact point K11 connected to subscriber line interface circuit 1 or turns on movable contact point K12 connected to ring bus 2.
When relay K2 is controlled to turn on movable contact point K22 connected to relay K3, the analog subscriber board realizes testing functions (testing the subscriber line, subscriber line interface circuit or ring), wherein when relay K3 turns on movable contact point K32 connected to subscriber line 4, the analog subscriber board realizes the function for testing the subscriber line; when relay K3 turns on movable contact point K31 connected to relay K2, the analog subscriber board realizes correspondingly the functions for testing the subscriber line interface circuit or testing the ring respectively according to that relay K1 turns on movable contact point K11 connected to subscriber line interface circuit 1 or turns on movable contact point K12 connected to ring bus 2.
Hence, the analog subscriber board realizes the various basic functions and the testing and monitoring functions by controlling the states of three relays respectively.
Three relays must be provided for each subscriber on this kind of analog subscriber board. However, relays occupy relatively large space, which is unfavorable for the design of the subscriber board. More essentially, relay has a high cost, for example, the relay of Fujistu FBR12ND04-P-25 type costs 3.6 yuan R.M.B. each. It is evident that the analog subscriber board having a less number of relay becomes the object of research of various providers because the manufacturing cost of the subscriber board is limited by the number of relays used.